DK147078B - METHOD FOR MAKING A CARBON FIBER WITH HIGH MODULUS AND HIGH STRENGTH - Google Patents

Description

ί

(19) DENMARK

| J | (12) PUBLICATION MANUAL OR 147078 B

DIRECTORATE OF

PATENT- 06 TRADE MARKET

(21) Patent Application No. 6426/74 (51) Int.CI.3: D01 F 9/12 (22) Filing Date: 10 Dec 1974 (41) Alm. available: 12 Jun 1975 (44) Submitted: 02 Apr 1984 (86) International Application No: - (30) Priority: 11 Dec 1973 US 423718 (71) Applicant: 'UNION CARBIDE CORPORATION; New York, US.

(72) Inventor: Irwin Charles * Lewls; US, Edgar Ronald 'McHenry; US, Leonard Sidney 'Singer; US.

(74) Plenipotentiary: Lehmann & Ree Engineering Company (54) Process for producing a high modulus and high strength carbon fiber

The invention relates to a process for producing a high modulus and high strength carbon fiber by spinning a carbonaceous fiber from a non-thixotropic carbonaceous mesophase beaker formed by heating a well-material which would form under calm conditions (non-stirring) a homogeneous bulk mesophase with large contiguous regions, heat curing of the thus-formed fiber in an oxygen-containing atmosphere for sufficient time to render it indigestible, and carbonizing the heat-cured fiber by heating it in an inert atmosphere.

As a result of the rapidly expanding growth of the aerospace engine, aerospace and rocket industries in recent years, there has been a need for materials that exhibit a special and extraordinary combination of physical properties. Thus, materials characterized by high strength and stiffness and at the same time low weight were required for such tt

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2 147078 areas such as the manufacture of airplane units and spacecraft, as well as in the manufacture of booths which could withstand the pressure of great depths and similar structures. Existing technology could not supply such materials, and research to meet this need was therefore focused on the production of composite articles.

One of the most promising materials proposed for compound use was high-strength and high modulus carbon textiles, which were introduced into the market at the same time as this rapid growth in the aerospace, aerospace and rocket industries found place. Such fabrics have been incorporated into matrices of both plastic and metal to form compositions with extraordinarily high ratios of strength and weight and modulus and weight, respectively, and with other excellent properties. However, the high cost of producing high strength and high modulus carbon textiles used in such composite products has hampered their spread despite the remarkable properties exhibited by such compositions.

A previously proposed method for providing high modulus and high strength carbon fiber at low cost is described in the specification of Danish Patent Application No. 4472/73. This method first comprises spinning a carbonaceous fiber from an earbonous pitch which has been partially converted to liquid crystal state or so-called "mesophase" state, then heat curing the thus-formed fiber by heating the fiber in an oxygen-containing atmosphere for sufficient time to render the non-fusible and final carbonization of the heat-cured fiber by heating in an inert atmosphere to a sufficiently high temperature to remove hydrogen and other volatiles and form a fiber of substantially pure carbon. The fibers thus formed have a highly oriented structure characterized by the presence of carbon crystallites, which are preferably aligned parallel to the fiber axis and are graphitizable materials which, when heated to graphitization temperatures, develop the three-dimensional order characteristic of polycrystalline graphite and its associated graphite-like properties, such as high density and low specific resistance. The fibers are characterized at all stages of their evolution from the drawn state to the graphitized state in the presence of large oriented, elongated graphitizable regions, which are preferably aligned parallel to the fiber axis.

When natural or synthetic pitch types with an aromatic base are heated under calm conditions at a temperature of about 3 ° C to 500 ° C either at constant temperature or at gradually increasing temperature, small insoluble liquid spheres begin to appear in the beaker and gradually grow by continued heating. When these spheres are examined using electron diffraction technique and polarized light, they are seen to consist of layers of oriented molecules directed in the same direction. As these spheres continue to grow, as the heating continues, they come into contact with each other and gradually fuse with each other to form large masses of unidirectional layers. As the fusion proceeds, regions of unidirectional molecules are formed that are much larger than the regions of the original spheres. These regions together form a mesophase in which the transition from one oriented region to another sometimes occurs smoothly and continuously over gradually curving slats and sometimes over more sharply curving slats. The different orientation of the regions, in polarized light, forms a complex grid of extinction contours in the mesophase corresponding to different forms of linear discontinuity in the molecular grouping. The final size of the oriented regions formed depends on the viscosity and the rate of viscosity increase of the mesophase from which they are formed, which in turn is dependent on the particular pitch and heating rate. In certain pitch types, areas with sizes from over 200 microns up to over 1000 microns are formed. In other pitch types, the viscosity of the mesophase is such that there is only limited fusion and structural rearrangement of the layers so that the final size of the regions does not exceed 100 microns.

The highly oriented, optically anisotropic, insoluble material formed by treating pitch in this way has been designated "mesophase" and pitch containing such material is known as "meophase pitch". When such pitch types are heated to above their softening points, they are mixtures of two substantially immiscible liquids, one being the optically anisotropic oriented mesophase portion and the other the isotropic non-mesophase portion. The term "mesophase" is derived from the Greek "mesos" or "intermediate" and denotes the pseudo-crystalline nature of this highly oriented, optically anisotropic material.

Carbonaceous pitch types having a mesophase content of from about 40% to about 90% by weight are suitable for fiber spinning, which can then be converted into carbon fibers with a high Young's modulus of elasticity and high tensile strength by heat treatment. However, in order to obtain the desired fibers from this pitch, it is not only necessary that this amount of mesophase be present, but also that under calm conditions it forms a homogeneous mesophase with large fused regions, i.e. areas of unidirectional molecules with a size from over 200 microns up to over 1000 microns. Beginning types that form triangular mesophase under calm conditions, having small oriented areas rather than large fused areas, are unsuitable. Such pitch types form a high viscosity mesophase, which undergoes only a limited fusion * insufficient to form large fused regions of sizes greater than 200 microns. Instead, small oriented mesophase regions agglomerate to form clumps or truncated masses in which the end region size does not exceed 100 microns. Certain pitch types that polymerize very quickly are of this type. Similarly, pitch types that do not form a homogeneous "bulk" mesophase are unsuitable. The latter phenomenon is caused by the presence of immiscible solids (either present in the original pitch or developed by heating) enclosed by the coalescing mesophase and causes a disruption of the homogeneity and uniformity of the fused regions and the boundaries between them.

Another requirement is that the beaker be non-thixotropic under the conditions used in the spin of the beaker to fibers, i.e. It Must . exhibit Newtonian or plastic flow properties so that the flow is smooth and good. When such pitch types are heated to a temperature at which they exhibit a viscosity of from ca. 10 poise to about 200 poise, uniform fibers can be easily spun from them. On the other hand, pitch types which do not exhibit Newtonian or plastic flow properties at the spinning temperature do not allow uniform fibers to be spun from them which, upon further heat treatment, can be converted into carbon fibers with a high Young's modulus of elasticity and high tensile strength.

Carbonaceous pitches having a mesophase content of from about 40% to about 90% by weight can be formed by the technique described in the specification of Danish Patent Application No. 4472/73, by heat treating a carbonaceous pitch in an inert atmosphere at a temperature above about 350 ° C for sufficient time to form the desired amount of mesophase. By inert atmosphere is meant an atmosphere which does not react with the beaker under the heat treatment conditions used, such as nitrogen, argon, xenon, helium, and the like. The heat treatment period needed to form the desired mesophase content varies with the particular pitch type and temperature used, with longer heat treatment periods being required at lower temperatures than at higher temperatures. At 350 ° C, which is the minimum temperature normally required to form mesophase, at least one week of heating is usually required to form a meso phase content of about $ 40. At temperatures of from 400 ° C to 450 ° C, conversion to mesophase progresses more rapidly, and a mesophase content of 50% can usually be formed at such temperatures in the course of approx. 1-40 hours. For this reason, such temperatures are normally used. Temperatures above about 500 ° C are undesirable and heating to this temperature should not be used for more than 5 minutes to avoid the conversion of the cup to coke.

When the beaker is heated to a temperature sufficiently high to form mesophase, the occurring, more volatile, low molecular weight molecules slowly evaporate from the beaker. As the heating is continued at a temperature above that at which mesophase is formed, they polymerize more reactive higher molecular weight molecules to form even higher molecular weight molecules which then orient to form mesophase. As mentioned earlier, this mesophase first appears in the form of small spheres of liquid which, as the heating proceeds, gradually grow and fuse with each other to form larger masses of mesophase. The fused masses have a density greater than the density of the non-mesophase portion and, as a result, tend to settle on the bottom of the reaction vessel as the polymerization progresses, while the lighter non-mesophase portion of the pitch tends to to ascend to the upper part of the container. After these fused mesophase masses are formed and settle on the bottom of the reaction vessel, the molecules therein which have a higher molecular weight than the molecules constituting the non-mesophase portion of the beaker continue to polymerize with each other to form molecules of even higher molecular weight. At the same time, the non-oriented molecules in the non-mesophase portion of the beaker in the upper portion of the reaction vessel continue to polymerize to form larger molecular weight molecules, some of which orient themselves to form mesophase, and some remain non-oriented. As more and more mesophase is formed by the polymerization of the more reactive molecules of greater molecular weight, it continues to gradually fuse and settle on the bottom of the reaction vessel, leaving the lower molecular weight molecules in the isotropic portion of the beaker in the upper portion of the reaction vessel.

Thus, this tendency of the immiscible mesophase and non-mexophase regions of the cup to be separated into two fractions during the formation of the mesophase is seen to result in the formation of a pitch having a high average molecular weight in the mesophase region and a low average molecular weight in mesofaseområdet. This unequal molecular weight distribution has been found to have an adverse effect on bone rheology and spinning ability, apparently due to the low compatibility between the mesophase portion of the pitch which is a very high molecular weight fraction and the non-mesophase portion of the pitch which is a very low molecular weight fraction. The very high molecular weight material in the mesophase portion of the beaker can only be sufficiently softened at very high temperatures, where the tendency for the very low molecular weight molecules in the non-mesophase portion of the beaker to advance is greatly increased.

In mesophase cup types with a mesophase content of at least 40% by weight prepared under calm conditions, i.e. in the absence of stirring, more than 80% of the molecules in the mesophase portion of the beaker have a molecular weight above 4000, while the remaining molecules have a number average molecular weight of 1400 to 2800. At the same time, the molecules in the non-mesophase portion of the beaker have a number average molecular weight of less than 800, and over 25% of these molecules have a molecular weight of less than 600. In general, the higher the mesophase content of the beaker, the wider the molecular weight distribution. When such pitch types are heated to a temperature at which they have a viscosity suitable for spinning, and attempts are made to form fibers thereof, there is a strong evaporation of volatiles, which greatly inhibits the processability of the small fiber pitch. and uniform diameter. For these reasons, attempts have been made to find methods for forming pitch types with a narrower molecular weight distribution, so that the beet achieves more favorable rheological properties, giving it better spinning properties, making it particularly suitable for spinning small and uniform diameter fibers.

Such a process is provided with the invention, which is of the kind referred to in the preamble, and which is characterized in that the well-being material is heated with stirring to a temperature of from 380 ° C to 440 ° C for such a period that a spinning mass having the following properties is obtained: 1: it is a homogeneous emulsion of the immiscible mesophase and non-mesophase portions of the beaker; 2: the mesophase content constitutes from 50 to 65% by weight of the beaker; 3: less than 50% of the molecules in the mesophase portion of the beaker has a molecular weight above 4000, 4: less than 20% of the molecules in the non-mesophase portion of the beaker have a molecular weight of less than 600, 5: the molecules in the mesophase portion of the beaker having a molecular weight below 4000 have a number average molecular weight of 1400 to 2800, 6: the molecules in the non-mesophase portion of the beaker have a number average molecular weight of from 800 to 1200.

7 147078

The stirring used in the process of the present invention should be sufficient to effectively mix the immiscible mesophase and non-mesophase portions of the cup. This stirring is readily accomplished by conventional means, e.g. by stirring or rotating the beaker.

Mesophase pitch types made according to the invention, i.e. thus, when stirring the beaker during the formation of the mesophase, there is a smaller difference between the number average molecular weights of the mesophase portion and the non-mesophase portion of the beaker, which is a consequence of a smaller amount of high molecular weight molecules in the beginning mesophase portion and a smaller amount of low molecular weight molecules in the beaker. the non-mesophase portion of the beaker and a lower number average molecular weight in the mesophase portion of the beaker and a higher number average molecular weight in the non-mesophase portion of the beaker than mesophase types with the same mesophase content produced without stirring.

Usually, from 20 to 40% of the molecules in the mesophase portion of the beaker have a molecular weight above 4000, while the remaining molecules have a number average molecular weight of from 1400 to 2600. The molecules in the non-mesophase portion of the beaker usually have a number average molecular weight of from 900 to 1200, and from 10 # to 16% of these molecules have a molecular weight of less than 600.

While any temperature from above about 350 ° C to about 500 ° C can be used to convert the precursor cup to mesophase, it has been found that heating at elevated temperatures changes the molecular weight distribution of both the mesophase portion and the non-mesophase portion of the beaker unwantedly, and that improved rheological and spinning properties are not achieved at such high temperatures. Thus, heat treatment at elevated temperatures tends to increase the amount of high molecular weight molecules in the mesophase portion of the beaker. At the same time, heat treatment at such temperatures also results in one increased amount of low molecular weight molecules in the non-mesophase portion of the beaker. As a result, mesophase cup types with a given mesophase content prepared at elevated temperatures over relatively short periods of time have been found to have a higher number average molecular weight in the beginning mesophase portion and a lower average molecular weight in the non-mesophase portion of the beaker than mesophase cup types with a corresponding mesophase content. produced at more moderate temperatures over longer periods. In order to maximize the reduction of the difference between the number average molecular weights of the mesophase portion and the non-mesophase portion of the pitch and to create pitch types with the most desirable rheological and spinning properties, the mesophase 8 is formed at temperatures of from 380 ° C to il40 ° C, preferably from 38 ° C to 410 ° C1 to form a mesophase content of from 50% to 65% by weight. Normally from 2 to 60 hours of heating is required at such temperatures to form the desired amount of mesophase. Mesophase pitch types prepared under these conditions have been found to have a smaller difference between the number average molecular weights of the mesophase portion and the non-mesophase portion of the beaker than mesophase cup types of the same mesophase content produced at higher temperatures over a shorter period of time. Therefore, such pitch types possess a smaller amount of molecules in the mesophase portion of the high molecular weight beaker and a smaller amount of molecules in the non-mesophase portion of the low molecular weight beaker, and have a lower number average molecular weight in the mesophase portion of the beaker and a higher number of non-molecular weight particles. the mesophase portion of the beaker than mesophase cup types with the same mesophase content that have been produced at higher temperatures over a shorter period of time.

In one embodiment of the method according to the invention, the beaker is subjected to reduced pressure during the formation of the mesophase, or an inert gas is passed through the beaker at this time. This embodiment has also been found to significantly reduce the time required to form a pitch with a given mesophase content at a given temperature.

When a carbonaceous pitch is heated to a temperature sufficiently high to form mesophase, the more volatile low molecular weight molecules that are present, as previously mentioned, slowly vanish from the beaker. As the heating is continued over a temperature at which mesophase is formed, the more reactive molecules of higher molecular weight polymerize to form molecules of even higher molecular weight, which then orient themselves to form mesophase. Although the less reactive, less volatile, less reactive molecules can also polymerize, they often form hydrogenated and / or substituted polymerization by-products with a molecular weight below about 600 that do not orient during mesophase formation. Although these low molecular weight polymerization by-products are volatilized as the heating of the beaker continues, the presence of large amounts of these by-products for a large part of the time during which the beaker is converted to mesophase has been shown to inhibit the formation of mesophase of the more reactive molecules. and, as a result, significantly prolong the time needed to form a pitch with a given mesophase content. Due to their small size and low aromaticity, these polymerization by-products are not readily reconciled with the larger, more aromatic, higher molecular weight molecules present in the early mesophase portion, and the incompatibility between these high and low molecular weight molecules affects beginning rheology and spinning ability undesirably. As previously pointed out, the fraction of the mesophase portion of the pitch having a very high molecular weight can only be sufficiently softened at very high temperatures, at which the tendency for very low mold weight molecules in the non-mesophase part of the pitch to volatilize is greatly increased, and when pitch types with large amounts of such materials are heated to a temperature at which they have a viscosity suitable for spinning and attempts are made to make fibers thereof, a vigorous expulsion of volatiles occurs, which greatly inhibits the processability of the cup. for fibers of small and uniform diameter.

By subjecting the beaker to reduced pressure during the formation of the mesophase or by passing an inert gas through the beaker at this time, one can take advantage of the differences in molecular weight and volatility between the mesophase-forming molecules present in the beaker and the components having low molecular weight and non-mesophase-forming polymerization by-products to achieve removal of the undesirable low-molecular-weight volatiles and more quickly convert the pitch to mesophase. The molecules that are not converted to mesophase are of lower molecular weight than the higher molecular weight mesophase-forming molecules and are preferably relieved by the vacuum present during the conversion of the pitch to the mesophase or by the flow of inert gas from the pitch to form the mesophase, which allows the beaker to achieve a given mesophase content in a significantly shorter time. Mesophase cup types having a meso-phase content of from about 50% to about 65% by weight can be prepared in this manner at a given temperature at a rate of up to more than twice that normally required in the absence of such treatment, i.e. at a time as short as less than half that normally required when forming mesophase in the absence of reduced pressure or without an inert gas passing through the beaker. Usually, the time required to form a pitch having a given mesophase content is reduced by at least 25%, usually from b0% to 705 when the mesophase is prepared under vacuum as described or when an inert gas is passed through the pitch as described, compared with when manufactured under identical conditions, but in the absence of such treatment.

Removal of the more volatile components of the beaker which is not converted into mesophase is accomplished by subjecting the beaker to a pressure of less than about 100 mm Hg, preferably less than 30 mm Hg, or by passing an inert gas through the beaker below the mesophase preparation at a rate of at least 31 liters per per hour kg of pitch, preferably at a rate of 44 to 31 liters per liter. per hour kg beg. Any inert gas which does not react with the pitcher under the heat treatment conditions used can be used to facilitate removal of these components. Examples of such gases are nitrogen, argon, xenon, helium, steam and the like.

Mesophase cups made in accordance with the invention generally have a viscosity of from 10 poise to 200 poise at a temperature of from 320 ° C to 440 ° C and at such temperatures can easily be spun into small and uniform diameter fibers with little volatility. Because of their extremely good rheological properties, such pitch types are particularly suitable for spinning carbonaceous fibers, which can then be converted by heat treatment to fibers with a high Young's modulus of elasticity and high tensile strength.

Bene's degree of conversion to mesophase can be easily determined by polarized light microscopy and solubility studies. With the exception of certain insoluble non-mesophase constituents present in the original pitch or in some cases developed by heating, the non-mesophase component of the pitch is readily soluble in organic solvents such as quinoline and pyridine, while the mesophase component is substantially ( 1) insoluble. v 'In the case of pitch types which do not develop insoluble non-mesophase constituents when heated, the insoluble content of the heat-treated pitch, in addition to the insoluble content of the pitch before being heated, corresponds essentially to mesophase- (2 ) the content. ν In the case of pitch types which do not develop insoluble non-mesophase constituents upon heating, the (1) The percent content of quinoline insoluble constituents (Q.I.) in a given pitch is determined by quinoline extraction at 75 ° C. The percent content of pyridine-insoluble constituents (P.I.) is determined by Soxhlet extraction in boiling pyridine (115 ° C).

(2) The insoluble content of the untreated pitch is usually less than 1% (except for certain coal tar types) and consists largely of coke and carbon black present in the original pitch.

11 147078 equal content of the heat-treated pitch in addition to the insoluble content of the beaker before it has been heat-treated not only transforms the beaker into mesophase but also represents the insoluble non-mesophase constituents which form together with the mesophase during the heat treatment. Batch types containing non-meltable insoluble non-mesophase constituents (either present in the initial pitch or developed by heating) in sufficient amounts to prevent the development of homogeneous bulk mesophase are unsuitable for use in the practice of the The present invention. Generally, pitch types containing more than about 2% by weight of such non-fusible materials are unsuitable. The presence or absence of such homogeneous bulk mesophase regions as well as the presence or absence of non-meltable insoluble non-mesophase constituents can be visually observed by polarized light microscopy examination (see, e.g., Brooks, JD and Taylor, GH, "The Formation of Some Graphitizing Carbons ", Chemistry and Physics of Carbon, Vol. 4, Marcel Dekker, Inc., New York, 1968, pp. 243-268 and Dubois, J., Agache, C. and White, J.L.," The Carbonaceous Me-sophase Formed in the Pyrolysis of Graphitizable Organic Materials ", Metallography 3, pp. 337-369, 1970). The amounts of each of these materials can also be determined visually in this way.

Conventional molecular weight analysis techniques can be used to determine the molecular weight properties of the mesophase pitch types formed in accordance with the present invention. In order to enable molecular weight determinations to be carried out independently on both mesophase and non-mesopha banknotes, the two phases can be suitably separated using a suitable organic solvent. With the exception of certain insoluble non-mesophase constituents which are present in the original pitch or which, in some cases, are developed by heating, the non-mesophase portion of the pitch as above is readily soluble in organic solvents such as quinoline and pyridine, while the mesophase portion is total Substantially insoluble. After separating the two phases with a solvent in this way, the non-mesophase portion of the beaker can be recovered from the solvent by vacuum distillation of the solvent.

A method that has been used to determine the number average molecular weight of mesophase pitch prepared according to the present (3) The non-mesophase part of the pitch can be easily separated from the mesophase part by extraction with quinoline at 75 ° C or by Soxhlet extraction in boiling pyridine.

The invention comprises the use of a vapor phase osmometer. Use of instruments of this type for molecular weight determination has been described by A.P. Brady et al. (Brady, A.P., Huff, H. and McGain, J.W., J. Phys.

& Coll. Chem. 5> 5, 304, (1951)) - The osmometer measures the difference in electrical resistance between a sensitive reference ether thermistor in contact with a pure solution and another thermistor in contact with a solution of said solvent in which a known concentration of a material whose molecular weight must be determined. The difference between the electrical resistance of the two thermistors is caused by a temperature difference between the thermistors, which is formed by the different vapor pressures of the solvent and the solution. By comparing this value with the differences in resistance obtained with said solvent and standard dop solutions of the solvent containing known concentrations of compounds of known molecular weight, it is possible to calculate the molecular weight of the solute. A drop of pure solvent and a drop of a solution of the solvent dissolving a known concentration of the material whose molecular weight is to be determined are suspended side by side on a reference ether thermistor and a sample ether mist contained in a closed thermostated chamber saturated with solvent vapor, respectively. , and the resistance of the two thermistors is measured and the difference between the two is determined. Since a solution of a given solvent will always have a lower vapor pressure than the pure solvent, there is a differential mass transfer between the two drops and the solvent vapor phase, which results in greater total condensation on (and less evaporation from) the solvent drop than on the solvent drop.

This difference in mass transfer causes a temporary temperature difference between the two thermistors (caused by the differences in evaporation heat loss between the two drops), which is proportional to the vapor pressure difference between the two drops. Since the vapor pressure difference between the two droplets and thus the temperature difference and the resistance difference (AR) between the two thermistors depends solely on the number of molecules of dissolved material dissolved in the solvent and is independent of the chemical composition of the molecules, the molar fraction, (N), can be dissolved. substance in the solution is determined from an image of AR vs. N for this solvent and solutions of this solvent containing known concentrations of compounds of known molecular weight.

(4) By the mole fraction of a given material in a solution (N) is meant the number of moles of this material in the solution divided by the number of moles of this material in the solution plus the number of moles of the solvent.

13 is a direct linear relationship to each other and from a determination of N it is possible to calculate the calibration constant (K) of the solvent used from the formula:

was

K - -N

After determining the value of K, the molecular weight of the material can be determined from the formula:

M · W

Μ = (K - AR) · -1 - x AR · Wv <y wherein M is the molecular weight of the material on which the determination is

X

made, K is the calibration constant of the solvent used, AR is the resistance difference between the two thermistors, M is the molecular weight of the solvent, Wy is the weight of the solvent and ΐίχ is the weight of the material whose molecular weight is to be determined. Once you have determined the value of the calibration constant "(K), for a given solvent, the molecular weight of a given material can of course be determined directly from the formula.

Although it is possible to determine the molecular weight of the soluble part of the beaker directly on a solution thereof, it is necessary to first solubilize the molecular weight of the insoluble part, e.g. by chemical reduction of the aromatic bonds of this material with hydrogen. A suitable method for solubilizing coal and carbon materials by reducing the aromatic bonds in these materials has been described by J.D. Brooks et al. (Brooks, J.D. and Sliber man, H., "The Chemical Reduction of Some Cokes and Chars", Fuel 4l, pp. 67-69, 1962). This process involves the use of hydrogen formed by reaction of lithium with ethylenediamine and has been found to effectively reduce the aromatic bonds in carbonaceous materials without breaking carbon-carbon bonds. This method has been used to solubilize the soluble portion of the pitch materials prepared according to the invention.

Another method that has been used to determine the molecular weight properties of mesophase pitch prepared according to the present invention is gel penetration chromatography (GPC). This technique has been described by L.R. Snyder (Snyder, LR, "Determination of Asphalt Molecular Weight Distributions by Gel Permeation Chromatography", Anal. Chem. 4_1, pp. 1223-1227 »1969) · A gel penetration chromatograph is used to fractionate a solution of polymer or polymer-like molecules of various sizes and the molecular weight distribution of the sample is determined by a detection system with a linear response to the solute concentration, such as a differential refractometer or an ultraviolet differential absorption spectrometer. To enable molecular weight determinations to be carried out independently on both the mesophase and non-mesophase portions of the beaker, the two phases, as in vapor phase osmometry, must first be separated using a suitable organic solvent. While the molecular weight of the soluble portion of the beaker can be determined directly on a solution thereof, again, to determine the molecular weight of the insoluble portion, it is first solubilized.

Fractionation of the sample whose molecular weight distribution is to be determined is performed by dissolving the sample in a suitable solvent and passing the solution through the chromatograph and collecting measured fractions of the solution eluting through the chromatograph's separation column. A given volume of solvent is required to pass molecules of a given molecular size through the chromatograph such that each fraction of solution eluting from the chromatograph contains molecules of a given molecular size. The fractions flowing through the column first contain the higher molecular weight molecules, while the longest fractions eluting through the column contain the lower molecular weight molecules.

After the sample has been fractionated, the concentration of solute in each fraction is determined by a suitable detection system, such as a differential refractometer or an ultraviolet differential absorption spectrometer. When a differential refractometer is used, the refractive index of each fraction is automatically compared to the refractive index refractive index by two photoelectric cells sensitive to the light intensity passing through these fractions and the solvent, and the differences in signal intensities between the two cells are automatically plotted against it. cumulative elution volume of the solution. Since the magnitude of these differences in signal intensity depends linearly on the weight concentration of molecules present, the relative weight concentration of molecules in each fraction can be determined by dividing the differential signal intensity of that fraction by the total integrated differential signal intensity of all the fractions. . This relative concentration can be graphically plotted by plotting the differential signal intensity for each fraction against the cumulative elution volume of the sample.

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The molecular weight of the molecules in each fraction can then be determined by a standard technique, for example, by the osmometry technique described above. Since most common start types are composed of uniform types of molecular groups, once the molecular weights of the various fractions of a particular sample have been determined, that sample can be used as standard and the molecular weights of subsequent samples can be determined from the known molecular weights. for corresponding fractions of the standard. Thus, molecular weight determinations need not be repeated for each fraction of each sample, but can be obtained from the molecular weights determined for corresponding fractions of the standard.

For convenience, a molecular weight distribution curve depicting the ratio of the molecular weight to the elution volume of the standard can be made by plotting the molecular weights determined for the standard fractions against the cumulative elution volume of the standard. The molecular weights of the molecules in the various chromatographic fractions of any given sample can then be read directly by this curve. As previously mentioned, the relative weight concentration of dissolved molecules in each fraction can be determined by refractive index differential measurements.

To facilitate molecular weight determinations, the differential signal intensities and elution volume values obtained for a given sample can be processed together with predetermined molecular weight data relating to the various chromatographic fractions of a standard pitch processed by a computer and transcribed into a complete molecular weight distribution analysis. This method routinely provides complete printouts of number average molecular weight (M), weight average molecular weight (M0), molecular weight distribution parameter (M / M) as well as molecular weight compilation and weight percent solute in each chromatographic fraction of a sample.

Carbonaceous base materials having an aromatic base having a carbon content of from about 92% to about 95% by weight and a hydrogen content of from about 4% to about 8% by weight are generally suitable for forming mesophase pitches which can be used to form fibers which are present in capable of being heat treated to form fibers with a high Young's modulus of elasticity and high tensile strength. Elements other than carbon and hydrogen such as oxygen, sulfur and nitrogen are undesirable and should not be present in amounts beyond about 4% by weight. The presence of more than this amount of foreign elements can destroy the formation of carbon crystallites during the subsequent heat treatment and impede the development of a graphite-like structure in the fibers made from these materials. Further, the presence of 'foreign elements' reduces the carbon content of the beaker and thus the final yield of carbon fiber. When such foreign elements are present in amounts of from about 0.5% to about 4% by weight, the pitch materials generally have a carbon content of from about 92 to 95% by weight, with the remainder being hydrogen.

Petroleum pitchers, coal tar pitches and acenaphthylene pitchers which are well graphitizing pitches are preferred starting materials for forming the mesophase pitch types used to make the fibers of the present invention. Of course, petroleum pitchers are the carbonaceous material: obtained from distillation of crude oils or catalytic cracking of petroleum distillates. Coal tar pitch is similarly provided by the distillation of coal. Both materials are commercially available natural pitch materials in which mesophase can be readily formed, and are preferred for this reason. Acenaphthylene pitch, on the other hand, is a synthetic pitch which is preferred because of its ability to form good fibers. Acenaphthylene pitch can be prepared by pyrolysis of polymers of acenaphthylene, as described by Edstrom et al. in the description to U.S.A. Patent No. 3 * 574,653 *

Certain pitch types, such as fluoranthene pitch, polymerize very rapidly when heated and do not develop large fused mesophase regions and are therefore not suitable precursor materials. Similarly, pitch materials having a high immiscible, insoluble non-mesophase content in organic solvents, such as quinoline or pyridine or those which develop a highly indigestible, insoluble non-mesophase content when heated, should not be used as starting materials as explained above, as these starting materials are unable to develop the homogeneous bulk mesophase needed to form highly oriented carbonaceous fibers capable of being converted by heat treatment to carbon fibers with a high Young's modulus of elasticity and high tensile strength. For this reason, pitch materials with an immiscible quinoline-soluble or pyridine-soluble content of more than approx. 2% by weight (determined as described above) is not used or should be filtered to remove this material before heating to form mesophase. Preferably, such pitch materials are filtered when they contain more than about 1% by weight of such immiscible, insoluble material. Most petroleum and synthetic pitch materials have a low immiscible and insoluble content and can be used directly without such filtration. Most coal tar materials, on the other hand, have a high immiscible and insoluble content and require filtration before they can be used.

Of course, when the beaker to form mesophase is heated to a temperature between 380 ° C and 440 ° C, it will pyrolyze to some extent, and the composition of the pitch will change depending on the temperature and heating time and on the composition and structure of the starting material. However, after heating a carbonaceous pitch for sufficient time to form a mesophase content of from about 50% to about 65% by weight, the resulting pitch will generally have a carbon content of about 94-96% by weight and a hydrogen content of about 4-6% by weight. . When such pitch materials contain elements other than carbon and hydrogen in amounts of from about 0.5 weight percent to about 4 weight percent, the mesophase pitch will generally have a carbon content of about 92 to 95 weight percent, with hydrogen remaining.

After the desired mesophase pitch has been produced, it is spun into fibers by conventional methods, e.g. by melt spinning, centrifugal spinning, blow spinning or in some other known manner. As indicated above, the beacon to obtain the highly oriented ear-containing fibers capable of heat treatment to form carbon fibers with a high Young's modulus of elasticity and high tensile strength should, under calm conditions, form a homogeneous bulk mesophase with large fused regions and not be -thixotrope under the conditions used in the spinning. In order to obtain uniform fibers from this pitch, the beaker should be further stirred immediately prior to spinning so that the immiscible mesophase and non-mesophase regions of the beaker are effectively blended together.

The temperature at which the cup is spun depends, of course, on the temperature at which the cup exhibits an appropriate viscosity. Since the bone softening temperature and its viscosity at a given temperature increase with increasing mesophase content and molecular weight of the beaker, the mesophase content and molecular weight should not be allowed to rise to a point which raises the softening point of the bone to a too high level. Pitches made according to the invention and having a mesophase content of about 50% by weight usually have a viscosity of about 200 poise at approx. 320 ° C and about 10 poise at about 400 ° C, while pitches having a mesophase content of about 65% by weight exhibit similar viscosities at about 370 ° C and 44o ° C, respectively. Within this viscous area, fibers can be suitably spun from such types at a rate of about 15 meters per minute. to about 305 meters per minute. and even up to 915 meters per minute. minute. The pitch used preferably has a viscosity of from about 30 poise to about 150 poise at temperatures from about 340 ° C to about 380 ° C. At this viscosity and temperature, uniform fibers with diameters of from about 5 microns to about 25 microns can be easily spun. However, as previously mentioned, in order to provide the desired fibers, it is important that the beaker be non-thixotropic and exhibit Newtonian or plastic flow properties during the spinning of the fibers.

The carbonaceous fibers thus produced are highly oriented graphitizable materials with a high degree of preferential orientation of their molecules parallel to the fiber axis. By "graffitiable" is meant that these fibers are capable of being thermally converted (usually by heating to a temperature above about 2500 ° C, e.g. from about 2500 ° C to about 3000 ° C) into a structure having the three-dimensional order characteristic of polycrystalline graphite.

The fibers thus formed have, of course, the same chemical composition as the pitch from which they were drawn, and, like this pitch, contain from about 50 weight percent to about 65 weight percent mesophase. When considered under magnification by microscopy techniques using polarized light, the fibers exhibit structural variations, giving them the appearance of "mini-composition". Large elongated anisotropic areas with a fibrillar appearance can be seen distributed throughout the fiber. These anisotropic regions are largely oriented and preferably aligned parallel to the fiber axis. It is believed that these anisotropic regions drawn long by the shear forces exerted on the pelvis during the spinning of the fibers do not consist solely of mesophase but also contain non-mesophase. Evidently, the non-mesophase is oriented as well as drawn to elongated regions during the spinning of these shear forces and the orientational stresses exerted by the mesophase regions while stretched long. Isotropic regions may also be present, although they may not be visible and difficult to distinguish from the anisotropic regions exhibiting extinction. Typically, the oriented elongated regions have diameters above 5000 Å, usually from about 10,000 Å to about 40,000 Å, and are easily observed because of their large size when examined by conventional microscopy technique using polarized light at a magnification of 1000.

19 147078

The maximum resolution of a standard microscope using polarized light with a magnification factor of 1000 is only a few tenths of a micron µl micron = 10,000 l / and anisotropic regions with dimensions of 1000 Å or less cannot be detected by this technique.

Due to the thermoplastic nature of the carbonaceous fibers made according to the present invention, it is necessary to heat cure these fibers before they can be carbonized. Heat curing of the fibers is easily accomplished by heating the fibers in an oxygen-containing atmosphere for sufficient time to render them indigestible. The oxygen-containing atmosphere used may be pure oxygen or an oxygen-rich atmosphere. Most suitably, air is used as the oxidizing atmosphere. Of course, the time required to obtain heat cure of the fibers will vary with such factors as the particular oxidizing atmosphere, the temperature used, the diameter of the fibers, the specific pitch from which the fibers are made, and the mesophase content and molecular weight distribution. in this pitch. In general, however, heat curing of the fibers can be accomplished in a relatively short time, usually from about 5 minutes to about 60 minutes.

Of course, the temperature used to obtain heat cure of the fibers must not exceed the temperature at which the fibers will become soft or change shape. Thus, the highest temperature that can be used will depend on the particular pitch from which the fibers were spun, and the mesophase content and molecular weight distribution of that pitch. The higher the mesophase content and the higher the average molecular weight of the beaker, the higher will be its softening temperature and the higher the temperature that can be used to obtain heat cure of the fibers. Of course, at higher temperatures, fibers of a given diameter can heat-cure in less time than is possible at lower temperatures. Fibers made from a pitch having a lower mesophase content and / or a lower average molecular weight, on the other hand, require relatively longer heat treatment at somewhat lower temperatures to render them indigestible.

A minimum temperature of at least 250 ° C is usually required to efficiently cure the carbonaceous fibers made in accordance with the invention. Temperatures above 400 ° C can cause melting and / or excessive burning of the fibers and should be avoided. Preferably temperatures of from about 275 ° C to about 350 ° C are used. At such temperatures, thermosetting can generally be accomplished in about 5 minutes to about 60 minutes. As it is undesirable to oxidize the fibers more than necessary to make them completely indigestible, the fibers are generally not heated for more than about 60 minutes or to temperatures above 400 ° C.

After the fibers have been heat cured, the hot-melt fibers are carbonized by heating in an inert atmosphere, such as that described above, to a temperature sufficiently high to remove hydrogen and other volatiles and form a fiber of substantially exclusively carbon. with a carbon content above about 98% by weight can generally be formed by heating to a temperature above about 1000 ° C and at temperatures above about 1500 ° C the fibers are completely carbonized.

Usually carbonization is carried out at a temperature of from about 1000 ° C to about 2000 ° C, preferably from about 1500 ° C to about 1900 ° C. Typically, residence times of from about 0.5 minutes to about 25 minutes are used, preferably from about 1 minute to about 5 minutes. Although longer-term heating times can be used with good results, such residence times are uneconomical and in practice there is no advantage to using such long periods.

To ensure that the weight loss rate of the fibers does not become so severe as to destroy the fiber structure, it is preferred to heat the fibers for a short period to a temperature of from about 700 ° C to about 900 ° C before heating to their final carbonization temperature. Residence times at these temperatures of from about 30 seconds to about 5 minutes are usually sufficient. Preferably, the fibers are heat treated at a temperature of about 700 ° C for about one minute and then to a temperature of about 900 ° C for the same time. In each case, the heating rate must be regulated in such a way that volatility does not occur at too high a rate.

In a preferred heat treatment method, continuous threads of the fibers are passed through a series of heating zones which are maintained at steadily higher temperatures. If desired, the first of these zones may contain an oxidizing atmosphere where the thermosetting of the fibers takes place. Numerous apparatus arrangements can be used to provide the range of heating zones. Thus, one furnace may be used, the fibers passing through the furnace several times and raising the temperature each time. Another possibility is that the fibers can make a single pass through several furnaces, each subsequent furnace being kept at a higher temperature than the previous furnace. Also, a single furnace 21 with multiple heating zones maintained at temperatures increasing in the direction of movement of the fibers can be used.

The carbon fibers thus produced have a highly oriented structure, characterized by the presence of carbon crystallites, which are preferably aligned parallel to the fiber axis, and are graphitizable materials which, when heated to graphitization temperatures, develop the three-dimensional order. which is characteristic of polycrystalline graphite and its associated graphite-like properties, such as high density and low electrically specific resistance.

If the carbonized fibers are further heated in an inert atmosphere, as described above, to an even higher temperature in a range from about 2500 ° C to about 3300 ° C, preferably from about 2800 ° C to about 3000 ° C, fibers are formed which not only have a high degree of preferential orientation of their carbon crystallites parallel to the fiber axis, but also a structure which is characteristic of polycrystalline graphite. A residence time of about 1 minute is satisfactory, however, both shorter and longer times can be used, e.g. from about 10 seconds to about 5 minutes or more. Stay times over 5 minutes are uneconomical and unnecessary but can be used if desired.

The fibers produced by heating to a temperature above about 2500 ° C, preferably above about 2800 ° C, are peculiar to the three-dimensional order of polycrystalline graphite. This three-dimensional order is detected by the X-ray diffraction pattern of the fibers, in particular by the presence of the (112) cross-grid line and the resolution of the (10) band in two distinct lines, (100) and (101). The short arcs constituting the (005) bands of the pattern show that the carbon crystallites of the fibers are preferably aligned parallel to the fiber axis. Microdensitometer scanning of the (002) band of the exposed X-ray film shows that this preferred orientation is not above about 10 °, usually from about 5 ° to about 10 ° (expressed as the full width at half the maximum azimuthal intensity distribution). Apparent layer size (L) and apparent stack height (L) for the crystallites are over 1000 Å and are thus too large to be measured by X-ray technology. The interlayer spacing (d) of the crystals, calculated from the distance between the corresponding (005) diffraction arcs, is not above 3S37 Å, usually from 3.36 Å to 3.37 Å.

EXAMPLES

The following examples are provided to illustrate the invention so as to be better understood by those skilled in the art. It should be noted that they serve as examples only and should not be construed as limiting the invention in any way.

EXAMPLE 1

PREPARATION OF MESO PHASE BAGS WHEN STIRRING

A commercial petroleum pitcher was used to make a pitch with a mesophase content of about 52% by weight. The precursorbegen had a number average molecular weight of 400, a density of 1.23 g / cc, a softening temperature of 120 ° C, and contained 0.83% by weight of quinoline insoluble ingredients (Q.I. was determined by quinoline extraction at 75 ° C). Chemical analysis showed a carbon content of 93.0%, a hydrogen content of 5.6%, a sulfur content of 1.1¾ and 0.044¾ ash.

The mesophase cup was prepared by heating 240 g of the precursor cup in a 350 ml container to a temperature of about 300 ° C over a period of 1 hour and then increasing the temperature of the pitch from about 300 ° C to about 400 ° C at a rate of about 60 ° C pr. and keep the beaker at about 400 ° C for an additional 17 hours. The beaker was stirred continuously after being heated to 300 ° C by a stirrer rotating at a speed of 300 rpm to form a homogeneous emulsion of the mesophase and non-mesophase portions of the beaker. Argon gas was continuously bubbled through the beaker throughout the experiment at a rate of 34 NL / h, while an additional stream of about 74 NL / h argon was passed through the dome of the vessel. After heating the beaker for 17 hours at 400 ° C, the beaker was cooled while stirring was continued.

Twelve (12.0) grams of the pitch thus prepared was then separated into mesophase and non-mesophase components by extracting the non-mesophase portion with boiling pyridine (115 ° C) in a Soxhlet extractor. The pyridine-soluble non-mesophase material (P.S.) was recovered from the pyridine by distilling the extract solution under reduced pressure to volatilize the pyridine. The recovered pyridine-soluble constituents were then, like the pyridine-soluble constituents (P.I.), dried in a vacuum oven at 110 ° C to remove traces of pyridine. Both materials were then weighed from which the beaker was determined to have a content of 52% by weight of pyridine-insoluble constituents (indicating a mesophase content close to 52¾).

Exactly 1.07 g of the pyridine-insoluble constituents were then solubilized by reducing the aromatic bonds of this material with hydrogen, generated by the reaction of lithium with ethylenediamine. The solid insoluble components were added to 65 ml of aqueous ethylene diamine and the resulting suspension was stirred and kept at a temperature of from 80 ° C to 90 ° C, while about 1.5 g of lithium was added over a period of 2 hours. . After the addition of lithium was complete, the whole mixture was heated under reflux for one hour. After this time elapsed, the mixture was cooled, poured over ice and acidified with concentrated hydrochloric acid. The acidified mixture was then centrifuged and a solid brown product collected. This material was washed repeatedly with distilled water until the wash water did not show conductivity (determined by a conductor's capability meter), and then filtered and dried. A total of 1.01 g of reduced pyridine-insoluble constituents was recovered, corresponding to a yield of $ 97.

The reduced pyridine-insoluble components were then extracted with boiling toluene. 61¾ of this material was found to be (5) soluble in toluene while the remaining $ 39 was insoluble. '

Gel penetration chromatographic determinations were performed on a toluene-soluble non-mesophase sample of the beaker and a toluene-solution reduced mesophase sample of the beacon (the toluene-soluble reduced pyridine-soluble portion of the beaker) using diluted toluene solutions of these materials. The measurements were made at 80 ° C using a chromatograph with a differential refractometer detector. The fractionation column had a distillation bundle equivalence of 244 bottoms. meters. About 50 chromatographic fractions were collected for each sample. Refractive index of each fraction was automatically compared to refractive index of the pure solvent by means of the reduced pyridine-soluble constituents, then extracted with boiling toluene. 61 $ of this material was found to be (B) soluble in toluene, while the remaining 39 $ was insoluble.

Gel permeation chromatographic determinations were performed on a toluene-soluble non-mesophase sample of the beaker and a toluene-solution reduced mesophase sample of the beacon (toluene-soluble reduced pyridine-soluble portion of the beaker) using diluted toluene solutions of these materials. The measurements were made at 80 ° C using a chromatograph with a differential refractometer detector.

(5) The insoluble material represents reduced pyridine insoluble constituents with a molecular weight above 4000, which is the upper molecular weight limit for toluene-soluble material.

24 147078

The fractionation column had an equivalent distillation plate number of 2 * 14 plates per meters. About 50 chromatographic fractions were collected for each sample. Refractive index of each fraction was automatically compared to refractive index of the pure solvent using two photoelectric cells sensitive to the light intensity passing through the fractions and solvent, and the signal intensity differences between the two cells were automatically plotted against the cumulative elution volume of the samples. to show the relative weight concentration of solute in each such fraction.

The number average molecular weight of 30 of the fractions was determined by vapor phase osmometry. From these determinations, a molecular weight distribution curve showing the relationship between the molecular weight and the elution volume of the samples was provided by plotting the molecular weight determined for the fractions against the cumulative elution volume of the samples. These curves were used as a standard in determining the molecular weights for the fractions of later samples.

These molecular weight data from the curves and GPC data were processed by a computer and transcribed for a complete molecular weight distribution analysis. The computer printout indicated the number average molecular weight (Mn) j the weight average molecular weight (M 1 (toluene-soluble, reduced pyridine-insoluble samples). The number average molecular weight of the toluene-soluble reduced mesophase sample (the toluene-soluble, reduced pyridine-soluble portion of the beaker) was found to be 2525 a while the weight average molecular weight of this material was found to be 2830. to 4000.

The number average molecular weight of the toluene-soluble non-mesophase sample was determined to be 640 and the weight average molecular weight was determined to be 677.

The beaker could be easily spun into fibers, and a significant amount of fibers 8 to 20 microns in diameter were made by spinning the beaker through a spinning hole plate (hole diameter 0.033 cm) at a temperature between 364 ° C and 370 ° C. As no spinning of the spinning hole plate was observed and very little evolution of volatiles during spinning, long spinning operations were possible without fiber break.

25 147078

Part of the fibers thus prepared were placed in an oven which had been preheated to 210 ° C. The oven temperature was then raised to 300 ° C at a rate of 4.3 ° C per hour. while oxygen was passed through the furnace at a flow rate of 0.2 l / min.

The resultant oxidized fibers were completely indigestible and could be heat treated at elevated temperatures without drift (downward). After heating the fusible fibers to 1900 ° C over a period of about 10 minutes in a nitrogen atmosphere, the fibers were found to have a tensile strength λ 2. 6 at 15.4 x 10 "^ kg / cm and a Young's modulus of elasticity of 3.0 x 10 kg / cin (tensile strength and Young's modulus are the mean values for 10 samples).

MESO PHASE PREPARATION WITHOUT STIRMING.

For comparison purposes, a mesophase beaker was prepared from the same precursor pitch in a manner similar to that described above, but without stirring. 253 g of the beaker was placed in a 350 ml reactor, covered with a watch glass, packed in a capsule and heated in an oven in an inert atmosphere to a temperature of about 40 ° C at a rate of about 60 ° C per minute. and maintained at this temperature for 8 hours.

A 13.0 g beaker with a pyridine-soluble content of 50¾ (indicating a mesophase content close to 50¾) was separated into mesophase and non-mesophase constituents and subjected to molecular weight determinations as described above. After reducing the pyridine-insoluble portion of the sample with hydrogen formed by reaction between lithium and ethylenediamine, the reduced pyridine-insoluble constituents were extracted with boiling toluene and found to contain 91¾ of toluene-insoluble material and only 9¾ of toluene-soluble (5) material.

Gel penetration chromatographic determinations showed that the number average molecular weight of the toluene-soluble reduced pyridine-soluble portion of the beaker (toluene-soluble, reduced mesophase sample of the beaker) was 2150, and the weight average molecular weight of this material was 2440.

The number average molecular weight of the toluene-soluble non-Meofase portion of the beaker was determined by gel penetration chromatography to 593j and the weight-average molecular weight was determined to 627 · Over 30¾ of the non-Meofase portion of the beaker (comprising toluene-soluble and toluene-insoluble material). over 4000, which is the upper molecular weight limit for toluene soluble material.

26 14,778 material) had a number average molecular weight of less than 600.

The beaker could not be spun into fibers with a diameter less than 40 microns, while fibers with a diameter greater than 40 microns were obtained with difficulty at temperatures around 380 ° C. Prolonged spinning operations were impossible due to frequent fiber breakage, caused by the beet clogging the spinning hole plate and by the strong evolution of volatiles during spinning.

EXAMPLE 2

380 ° C HEAT TREATED BEG

A commercial petroleum pitcher was used to produce a pitch with a mesophase content of about 56% by weight. The precursorbegen had a number average molecular weight of 400, a density of 1.23 g / ec., A softening temperature of 120 ° C and contained 0.83% by weight of quinoline-soluble ingredients (Q.I. was determined by quinoline extraction at 75 ° C). Chemical analysis showed a carbon content of $ 93.0, a hydrogen content of 5.6%, a sulfur content of 1.1¾ and 0.044¾ ash.

The mesophase beaker was made by heating 29.5 kg of the precursor oil beaker in a 26.5 liter container to a temperature of 380 ° C at a rate of about 100 ° C per minute. hour and keep the beaker at this temperature for another 51 hours. The beaker was continuously stirred during this time by a stirrer rotating at a rate of 700-1200 rpm to form a homogeneous emulsion of the mesophase and non-mesophase portions of the beaker. Nitrogen gas was continuously bubbled * 2 through the beaker throughout the course at a rate of 1.42 Nnr / h.

5.0 g of the pitch thus formed was then separated into mesophase and non-mesophase constituents by extracting the non-mesophase portion with boiling pyridine (115 ° C) in a Soxhlet extractor. The pyridine-soluble non-mesophase material (P.S.) was recovered from the pyridine by distilling the extract solution under reduced pressure to volatilize the pyridine. The recovered pyridine-soluble constituents were then dried, like the pyridine-soluble constituents (P.I.), in a vacuum oven at 110 ° C to remove traces of pyridine. Both materials were then weighed from which the beaker was determined to have a content of 56% by weight of pyridine-insoluble constituents (indicating a mesophase content close to 56¾).

1.00 grams of the pyridine-insoluble constituents were then solubilized by reducing the aromatic bonds of this material with hydrogen formed by the reaction of lithium with ethylene diamine. The solid insoluble components were added to 65 ml of anhydrous ethylenediamine and the resulting suspension was stirred and maintained at a temperature of 80 ° C-90 ° C while about 1.5 g of lithium was added over a period of 2 hours. After the addition of lithium was complete, the whole mixture was heated under reflux for one hour. At the end of this time, the mixture was cooled, poured over ice and acidified with concentrated hydrochloric acid. The acidified mixture was then centrifuged and a solid brown product collected. This material was washed repeatedly with distilled water until the wash water did not show conductivity (determined by a conductivity meter) and then filtered and dried. A total amount of 0.96 g of reduced pyridine-insoluble constituents was recovered, yielding a yield of 96¾.

The reduced pyridine insoluble components were then extracted with boiled toluene. 68% of this material was found to be soluble in toluene, while the remaining 32% was insoluble.

Gel penetration chromatographic determinations were performed on a toluene-soluble non-mesophase sample of the beaker and a toluene-soluble reduced mesophase sample of the beaker (toluene-soluble, reduced pyridine-soluble portion of the beaker) using diluted toluene solutions of these materials as described above. These GPC data and molecular weight data from the molecular weight distribution curve described in Example 1 were processed by a computer and transcribed for a complete molecular weight distribution analysis. The computer printout provided the number average molecular weight (M), the weight average molecular weight (MTT), the molecular weight distribution parameter (M / M) and a compilation of the molecular weight and weight percent solute present in each chromatographic fraction of both toluene-soluble, non-soluble, non-mesophase-soluble and toluene-soluble, samples). The number average molecular weight of the toluene-soluble reduced mesophase sample (toluene-soluble, reduced pyridine-soluble portion of the beaker) was found to be 2620, while the weight average molecular weight of this material was found to be 2980.

The number average molecular weight of the toluene-soluble non-mesophase sample was determined to be 616, and the weight average molecular weight was determined to be 652. Less than 16% of the non-mesophase portion of the beaker (comprising toluene-soluble and toluene-soluble material) had a number-average molecular weight The mesophase portion of the beaker, determined by vapor phase osmometry on a pyridine-soluble sample of the beaker, was found to be 1040.

The beaker could be easily spun into fibers, and a significant amount of fibers of 8-20 microns in diameter were prepared by spinning the beaker through a 41-hole spinning hole plate (0.015 cm hole diameter) at a rate of about 226 m / min. between 350 ° C and 380 ° C. The threads passed through a nitrogen atmosphere as they left the spinning hole plate and before being recorded on a spool. As no obstruction of the spinning hole plate was observed and only very little development of volatiles during spinning, long spinning operations were possible without fiber break.

Part of the fibers thus prepared were heated to 298 ° C in air at a rate of 6 ° C per minute. The resulting oxidized fibers were completely indigestible and could be heat treated at elevated temperatures without drifting. After heating the fusible fibers to 1800 ° C over a period of about 60 minutes in a nitrogen atmosphere, the fibers were found to have a tensile strength of 17 x 10 6 kg / cm

Young's modulus of elasticity of 1.5 x 10 kg / cm. Tensile strength and Young's modulus are the average values for 10 samples).

450 ° C HEAT TREATED BEG

In comparison, a mesophase beaker was prepared from the same precursor pitch and in the same manner as described above except that the beaker was heated to 450 ° C at a rate of 100 ° C per minute. hour and kept at this temperature for 1 ^ hour. The resulting pitch had a pyridine-soluble content of 57%, indicating a mesophase content of close to 57%.

A portion of the beaker was separated into mesophase constituents and non-mesophase constituents and subjected to molecular weight determinations as described above. After reducing the pyridine-insoluble portion of the beaker with hydrogen formed by reaction of lithium with ethylenediamine, the reduced pyridine-insoluble ingredients were extracted with boiling toluene and found to contain $ 82 toluene-insoluble material and only $ 18 (5) toluene-soluble material.

Gel penetration chromatographic determinations showed that the number average molecular weight of the toluene-soluble, reduced pyridine-soluble portion of the beaker (toluene-soluble, reduced mesophase sample of the beaker) was 2190, and that the weight average molecular weight of the material was 2640.

The number average molecular weight of the toluene-soluble non-meofase portion of the beaker was determined by gel penetration chromatography to be 583 and the weight average molecular weight was determined to be 617 · More than $ 25 of the non-mesophase portion of the beaker (comprising toluene-soluble and toluene-soluble material). 29 than 600. The number average molecular weight of the entire non-mesophase portion of the beaker, determined by vapor phase osmometry on a pyridine-soluble sample of the beaker, was found to be 730.

The beaker could not be spun into fibers with a diameter less than 40 microns, while some fibers having a diameter above Ho microns were difficult to obtain at temperatures of about 370 ° C. Prolonged spinning operations were impossible due to frequent fiber breakage caused by the clogging of the spinning device and the excessive development of volatiles during spinning.

Claims (4)

30 147078 Patent Claims. A process for producing a high modulus and high strength carbon fiber by spinning a carbonaceous fiber from a non-thixotropic carbonaceous mesophase beaker formed by heating a well-material which would form a homogeneous bulk mesophase under calm conditions (non-stirring) with large seam-hung areas, heat curing of the thus-formed fiber in an oxygen-containing atmosphere for sufficient time to render it indigestible, and carbonation of the heat-cured fiber by heating it in an inert atmosphere, characterized in that the comfortable material is heated with stirring. to a temperature of from 380 ° C to 440 ° C for such a time as to obtain a spinning mass having the following properties: 1: it is a homogeneous emulsion of the immiscible mesophase and non-mesophase portions of the beaker; 2: the mesophase content constitutes from 50 to 65% by weight of the beaker, 3: less than 50% of the molecules in the mesophase portion of the beaker have a molecular weight above 4000, 4: less than 20% of the molecules in the non-mesophase portion of the beaker has a molecular weight of less than 600, 5: the molecules in the mesophase portion of the beaker having a molecular weight below 4000 have a number average molecular weight of from 1400 to 2800. 6: the molecules in the non-mesophase portion of the beaker have a number average molecular weight of from 800 to 1200. The method according to claim 1, characterized in that not more than 40% of the molecules in the mesophase part of the pitch have a molecular weight above 4000 and that not more than 16% of the molecules in the non-mesophase part of the pitch have a molecular weight of less than 600. Method according to claim 2, characterized in that the molecules in the mesophase part of the beaker having a molecular weight below 4000 have a number average molecular weight of 1400 to 2600 and the molecules in the non-mesophase part of the beaker have a number average molecular weight of 900 to 1200. . Process according to claims 1-3, characterized in that the beaded material is heated with stirring at a temperature of from 380 ° C to 410 ° C to form the homogeneous emulsion of the immiscible mesophase and non-mesophase parts of the beaker .